U$6$L $4$ Writing Ionic Formulas

Content Objective: SWBAT $1.$ describe ionic formulas $2.$ explain the steps in writing formulas for ionic compound $3.$ explain in terms of charge why ions form these compounds.

Language Objective: Students will use elaboration and description language to describe chemical formulas, sequencing language to explain the steps in writing formulas, and cause and effect language to explain why these ions form these compounds.

Do Now: Read and annotate the following paragraph using the UCQ method.

As we have seen in the lonic Bonding Lab, ionic compounds form to have a net zero or neutral charge overall. While we used the puzzle pieces to model this in the lab, there is another strategy we can use to predict the formula of ionic compounds known as the Criss Cross method. First, we must determine the charge of each ion present. Group $1$ and $2$ metals tend to form only one type of ion, whereas transition metals often form more than one. We use a Roman numeral in parentheses to indicate the charge on a transition metal. Once we know the charges we move the charge of the cation down to become the anion's subscript, dropping the $+$ sign in the process. We then do the same, moving the anion's charge to become the cation's subscript, dropping the $-$ sign in the process. Thus, the charges are Criss Crossed to find our formula. If needed, we simplify these subscripts.

Central Idea:

Question$($s$)$:

Activity $1$:

Explain how to use the Criss Cross method to determine an ionic formula.

Use your Periodic Tables and the Criss$-$Cross Method to determine the correct ionic formula for the following pairs of metals and nonmetals. Show all work!

Lithium & Fluorine

Li

Strontium & Iodine

Potassium & Nitrogen

Magnesium & Sulfur

Aluminum & Phosphorus

Calcium & Hydrogen